From: Ahmed Mamoor Amimi (mamoor@xxxxxxxx)
Date: Thu Mar 21 2002 - 06:31:15 GMT-3
Hi,
I have collected some ATM facts and notes..... may be of some interest.
FACTS:
-ATM combines the benefits of Circuit and Packet Switching
-ATM is connection oriented
-VPI-VCI makes a full virtual circuit
-Each VC is a p-t-p and is bidirectional
-ATM dont know what is data but know that packet is coming to ATM
processor and is formated accordingly to AAL format
-AAL1 and AAL2 carries traffic such as Voice and Video
-AAL3,4,5 is for data communication that is segment and reassemble but
not the AAL1 and AAL2
-For broadcast a VC is reserved so when any switch recieve the data
on that VC it duplicate the packet and send it to all the VCs it have
-ATM-DXI = ATM-data exchange interface
-ATM-DXI support multiprotocol on one PVC or on multiple
-Interim Local Management Interface (ILMI)
-ILMI is used to discover PVCs fromt the switch and this is not to map
ip to PVC. For this maping normal inverse arp is used which is enable
by default.If static map is configured them IARP is off. and is only for
IP&IPX
-The ilmi is only used on main interface to flow the PVC to sub-int later
-default ilmi keepalive is 3sec
-All ATM interfaces are full duplex
-physical layer interface module (PLIM)
-ATM support following encapsulation:
LLC/SNAP(Multiprotocol encapsulation in one PVC)---new
MUX (one protocol per PVC)
NLPID (Multiprotocol encapsulation in one PVC)--old
QSAAL (used with SVCs for setting up and tearing down VC)
SMDS
PPPoATM
-vpi/vci
-default encapsulation is LLC/SNAP
-If the network's pricing depends on the number of PVCs set up, snap
might be the appropriate choice. If pricing depends on the number of
bytes transmitted, mux might be the appropriate choice because it
has slightly less overhead.
-VC can be p-t-p and p-t-m
-Pseudobroadcast for Multicast packets
-Fast switching is enabled be default
-if there is no ARP resolution on ATM then we have to define ATM and IP
address on both ends
-in-band signalling = connection establishment done on the same circuit as
data transfer
-ESI = Endstation ID
-ESI address is 12 HEX char equal to mac address and a selector byte (2 HEX)
-The atm nsap-address and atm esi-address commands are mutually exclusive
-Service-Specific Connection-Oriented Protocol (SSCOP)
-Service-specific convergence sublayer (SSCS)
-U can close an idle SVC by command : atmsig close atm 1 VCD
-U call apply a VC to main,sub,pvc and svc interface
-all the parameters that can be applied to main is allowed in vc-class
-if any SVC command in vc-class is applied and called in PVC it is
ignored and that is same with SVC
-ILMI and OAM (operation,administration and management) is the two method
of monitoring and detecting broken PVC or SVC. These are used to reroute
the packet to other PVC with less time-out
-If both are configured on a interface then pvc will comes up when both
indicate UP. so be carefull when applying both.
-ATM ARP server will tear down the ARP connection but client will attemp
to bring the connection UP every minute
-Router can act as both ARP server and client but should be on same subnet
-When ESI is used the ATM switch must be capable to give NSAP address
to the router.
-In PVC enviroment ATM inverse ARP is enabled by default for IP and IPX
-to set the inverse ARP refrest time use inarp 5 (min). 15 is default
-Rate queue is the peak rate at which a PVC will trasmit "atm rate-queue"
-The combine of all the rate queue should not exceed the total bandwidth
-Max MTU of ATM is 4470 can be altered by "MTU xxx"
-loopback all the incoming packet back to the network "loopback line"
-limiting the # of VC on interface "atm maxvc xxx"
-There can be 1024 vci to built a vpi, u can limit this to save buffer
by using command "atm vc-per-vp xxxx"
-to generate the clock locally use "atm clock internal"
-U can also using bridge under ATM. use the same old command "bridge group
xx"
-The multiplex (MUX) option defines the PVC to carry one protocol only;
each protocol must be carried over a different PVC. The Subnetwork Access
Protocol (SNAP) option is LLC/SNAP multiprotocol encapsulation, compatible
with RFC 1483; SNAP is the current default option. The network layer
protocol
identification (NLPID) option is multiprotocol encapsulation, compatible
with RFC 1490; this option is provided for backward compatibility with the
default setting in earlier versions in the Cisco IOS software.
-In the event of failure, the router responds with one of two methods.
The first method dynamically assigns the traffic bound on the failed
VC to an alternative VC, which is termed circuit bumping.
-Mamoor
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